Hypersensitivity and Autoimmunity

Question 1

4 types of immune response

Answer 1

1 - IgE mediated reactions
2 - cytolytic or cytotoxic reactions
3 - immune complex reactions
4 - cell mediated immunity reaction

Question 2

Type I - mechanism of sensitisation phase

Answer 2

• Exposure to allergen activates T helper 2 cells that stimulate B cells to form IgE producing plasma cells
• IgE produced in response to antigenic stimulus and binds to Fc receptors on mast cells and basophils

Question 3

Type I - mechanism of activation phase

Answer 3

• Re-exposure to antigen triggers mast cells and basophils to respond by release of their granules containing histamine

Question 4

Type I - mechanism of effector phase

Answer 4

 Complex response occurs because of histamine and other pharmacologically active agents released by mast cells and basophils
(smooth muscle contraction and vasodilation mong others)

Question 5

systemic effects of histamine

Answer 5

GI tract - increased fluid secretion, increased peristalsis
Airways, nasal passages - decreased diameter, increased mucus secretion
Blood vessels - increased blood flow, increased permeability

Question 6

systemic type 1 reaction

Answer 6

anaphylaxis
shock like and often fatal
smooth muscle contration and systemic vasodilation
treated with adrenaline

Question 7

localised type 1 reaction

Answer 7

allergic rhinitis (hay fever)
asthma
atopic dermatitis
food allergies

Question 8

late phase in type 1

Answer 8

occurs 3-9 hours after immediate response

caused by sustained activation of mast cells. can lead to a Type 4 hypersensitivity

Question 9

detection of type 1 responses

Answer 9

wheat and flare - allergen injected under skin, red and lumpy after 15 for a positive test
Specific IgE - serum sample assesed for a pre-determined allergy

Question 10

treatments of type 1

Answer 10

avoidance
anti histamines
cromolyn chloride
corticosteroids
theophylline
adrenaline for anaphylaxis
desensitisation - inject with increasing doses over time

Question 11

Type II

Answer 11

antibody dependant cytotoxic hypersensitivity - ADCC
mediated by IgM and IgG
haemolysis
3 types - blood transfusions, haemolytic disease of the newborn, and drug induced haemolytic anaemia

Question 12

mechanism of ADCC

Answer 12

antibody binds to antigens on the surfae of target cells
Fc receptors on NK cells recognise bound Ab
crosslinking of Fc receptors signals the NK cell to kill the target cell
cell dies by apotosis

Question 13

Type III - mechanism

Answer 13

reaction of Ab withantigens creates immune complexes facilitating the clearance by phagocytotic cells and mast cell activation
hoever, large amounts of these complexes can lead to tissue damaging type III reactions

Question 14

type III - examples

Answer 14

farmers lung - inhalation of actinimyocytes from mouldy hay
pigeon fanciers lung - from their faeces
serum sickness - upon administration of anti-tetanus/diphtheria meds, large amounts of antigen and therefore immune complexes enter bloodstream

Question 15

type IV

Answer 15

delayed type hypersensitivity - DTH
localised inflammatory response caused by Th cells
large influx of inflammatory cells and macrophages
is often helpful, but can also cause tissue damage
e.g. herpes, measles, hair dyes, poison ivy

Question 16

type IV - mechanism

Answer 16

APC stimulate Th1 cells for the first time, then migrate to site where antigens are localised
influx and activation of macrophages in DTH response is good, but if antigen acn’t be cleared quickly, prolonged DTH response causes continuous activation of macrophages
leads to granulomas forming, and tissue damage

Question 17

example of each type of hypersensitivity

Answer 17

I - anaphylaxis, hay fever, asthma, food allergies
II - ADCC, anaemia, grave’s disease, myasthenia gravis
III - SLE (lupus)
IV - MS

Question 18

predisposing genes

Answer 18

IL-2R and IL-7R - MS
IL-23R - Crohn’s
HLA - autoimmunity

Question 19

treament of autoimmune disease

Answer 19

immunosuppression
plasmapheresis
IV Ig
stem cell transplantation